1. Technical Field
This invention relates generally to telecommunications switching systems, and more particularly, to an apparatus and method for managing switching exchange resources.
2. History of Related Art
Telephony, like the mails, provides individual, person-to-person communication. The overall circuit between one subscriber and another may change from call to call. Switching exchanges make possible the rapid and drastic reconfiguration of the transmission path that constitutes the telephone connection network. During periods of average usage, telephone exchanges are not utilized at anywhere near their full capacity. However, during times of high traffic volume, or peak times, the number of resources available in any particular exchange is dramatically reduced, and idle resources may be non-existent.
Ongoing, or completed, calls are not the only system activity which occupies exchange resources. Any time a call is placed, there must be some partial occupation of system resources until the call is completed. The time required to place a call is divided up into three periods: (1) that time occupied by the dial tone (i.e. the dial tone delay), (2) that time occupied by dialing (i.e. the dialing delay), and (3) that time occupied by the ring tone (i.e. the ring tone delay). Such call placement activities and other, less usual, events (e.g. forgotten links which are left connected for longer than a few hours) may account for significant occupation of system resources. In addition, some system delays, such as busy signals and off-hook conditions, occupy exchange resources and never result in call completion.
While safeguard timers have been built into exchange switches to time-out under various circumstances, during periods of high traffic volume such constraints may be inadequate to produce the most efficient use of switching resources. For example, it is quite common for a subscriber to leave the phone in an off-hook condition, where it remains producing a dial tone until the related timer within the exchange switch expires (i.e. times-out). Similarly, when a subscriber attempts to call another who is absent or does not answer the phone, the ring tone is often asserted for much longer than necessary. Common time-out delays within exchange switches are forty five seconds for the dial-tone and ninety seconds for the ring tone. It is not until the respective timers in the exchange switch time-out that associated system resources are freed and made available for other subscribers. These timers, which operate within the exchange switch, also fail to react to changing load conditions and call placement activities which seize system resources for extended time periods.
One approach to solving a portion of this problem utilizes an electronic circuit capable of releasing a channel and trunk in a telephone central office by inserting an additional timer between the telephone and the central office. The timer senses the commencement of the dial tone and opens the tip or ring lead whenever an off-hook condition persists for more than about fifteen seconds without the commencement of any dialing activity. However, this limited approach is not sensitive to loading conditions within the exchange switch and only operates to minimize a single resource-consuming activity which can occur during call placement.
A method and apparatus capable of monitoring the loading conditions within an exchange switch is needed so as to actively adjust the time-out safeguards applied to call placement activities, and other activities, as mentioned previously, so as to more efficiently utilize switching resources. Further, it is at times desirable to manage switching resources in a proactive or anticipatory fashion, rather than in a reactive fashion. That is, some periods of high traffic volume are completely predictable (e.g. business hours and holidays); such peak periods can be anticipated and better-accommodated by adjusting the time-out safeguards built into the exchange switch. New timers may also be introduced into switching exchanges for further efficiency. Finally, it is also desirable to provide switching exchange management in a completely uncoordinated and independent fashion, so as to accommodate switching equipment from different manufacturers without regard to specific protocols or signaling. It is also desirable to provide coordinated switching for circumstances involving unified network signaling protocols which can be adapted to provide loading information and time-out period adjustment along the entire length of each call signal path.
The invention basically comprises a timer and a timer reduction unit within a switching exchange which adjust measured time-out values and thus control switching exchange resource availability in an intelligent fashion. For example, the timer within the exchange may be set to measure a predetermined usage time for an exchange resource. Such timers include a dial tone timer, a dialing timer, a ring tone timer, or a busy signal timer. When a predetermined condition is detected, the timer reduction unit may act to reduce the measured predetermined usage time for the switching exchange resource, causing a time-out to occur sooner. This reduction may be by a percentage amount or by a predetermined amount of time, such as a fixed number of seconds.
The predetermined condition may be a loading condition, such as the number of occupied switch resources, the number of calls active within the exchange, the number of calls occurring within a predetermined amount of time, or the number of active ports or switches. The predetermined condition may also be a timing condition, such as the time of day, or the date. Finally, the predetermined condition may be an event, such as the occurrence of repairs at a particular exchange, or the installation of a new exchange.
In accord with another aspect of the invention, the timer and timer reduction unit may also exist within a Private Branch Exchange (PBX). The predetermined conditions applicable to a switching exchange also apply to implementation of the invention within a PBX.
In accord with another aspect of the present invention, a telecommunications system may comprise a first and second switching exchange connected by a communications link. Upon detection of a predetermined condition by the second exchange, a signal may be sent from the second exchange to the first exchange so as to reduce the predetermined usage time of a timer in the first exchange. Again, the predetermined condition at the second exchange which triggers a response by the timer reduction unit in the first exchange may be implemented as described above. Of course, the second switching exchange may also act to reduce an internal timer predetermined usage time, and relay a message to other exchanges along the call connection path so as to communicate the fact that the call may be dropped by the second exchange before active timers in the other connected exchanges have timed-out.
Finally, the invention embodies a method of operating a switching exchange comprising the steps of: sensing an existing condition, such as an existing loading condition, timing condition, or event; comparing the existing condition with a predetermined condition; and then reducing the value of the predetermined usage time for a switching exchange resource timer if the existing condition is equal to the predetermined condition value. For example, if the predetermined condition is a loading condition, such as 90% occupation of switching matrix ports, and 90% of the ports are actually occupied as the existing condition, then the ring tone timer within the exchange may have its value reduced from 90 seconds to 75 seconds. All of the discussion above with respect to the variety of predetermined conditions applies with equal force to the method of the invention.